JP6253326B2 - Light source and optical coherence tomography apparatus using the light source - Google Patents

Description

  The present invention relates to a light source and an optical coherence tomography apparatus using the light source.

  A super luminescent diode (hereinafter sometimes abbreviated as SLD) has a broad spectrum distribution like a light emitting diode, but can obtain a relatively high light output of 1 mW or more like a semiconductor laser. A semiconductor light source. SLD attracts attention in the medical field and measurement field where high resolution is required due to its characteristics. For example, SLD is used as a light source of an optical coherence tomography (OCT) apparatus capable of acquiring a tomographic image of a living tissue. It is done.

  For acquiring a high-resolution tomographic image, it is preferable to use a light source that emits light with an emission spectrum having a wide full width at half maximum. Examples include using two asymmetric multiple quantum well structures having different quantum well widths as described in Non-Patent Document 1, a plurality of quantum well structures having different composition ratios, and an active layer having a single quantum well structure. These structures are intended to obtain a wide spectrum full width at half maximum by using superposition of emission spectra from different energy levels.

IEEE Photonics Technology Letters, vol. 8, no. 11, pp. 1456-1458, 1996

  However, in Non-Patent Document 1, a broad spectrum can be obtained by increasing the amount of current injection, but the spectrum half-width is limited by the gain spectrum and device structure of each quantum well. Therefore, the SLD described in Non-Patent Document 1 cannot emit light with an emission spectrum having a sufficiently wide full width at half maximum.

  In view of the above problems, an object of the present invention is to provide a light source that emits light with an emission spectrum having a wider full width at half maximum.

A light source according to the present invention includes a superluminescent diode having one or more light emitting regions and an emission spectrum conversion region, and a control for controlling a current injected into the one or more light emission regions and the light emission spectrum conversion region. A light source having a portion,
Light emitted from one first light emitting region of the one or more light emitting regions, the light passing through the light emission spectrum conversion region, and from the first light emitting region, or the one or more light emitting regions. The light emission region is configured to be combined with light emitted from a second light emission region different from the first light emission region and not passing through the light emission spectrum conversion region,
The control unit controls a current injected into the emission spectrum conversion region and the first emission region so that a current density of the emission spectrum conversion region is smaller than a current density of the first emission region. It is characterized by that.

  According to the light source of the present invention, it is possible to provide a light source that emits light with an emission spectrum having a wider full width at half maximum by using light generated in the emission region and passing through the emission spectrum conversion region. .

It is a figure for demonstrating the light source which concerns on embodiment of this invention. It is (a) perspective view (b) top view for demonstrating the light source which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the layer structure of the light source which concerns on Embodiment 1 of this invention. It is (a) perspective view (b) top view for demonstrating another example of the light source which concerns on Embodiment 1 of this invention. It is (a) perspective view (b) top view for demonstrating the light source which concerns on Embodiment 2 of this invention. (A) Perspective view for explaining a light source according to Embodiment 3 of the present invention (b) Plan view seen from point X (c) Plan view seen from point Y It is (a) perspective view (b) top view for demonstrating the light source which concerns on Embodiment 4 of this invention. It is (a) perspective view (b) top view for demonstrating the light source which concerns on Embodiment 5 of this invention. It is a figure for demonstrating the OCT apparatus which concerns on Embodiment 6 of this invention. It is a graph which shows the emission spectrum obtained from the light source produced in Example 1 of this invention. It is a figure for demonstrating the procedure which produces a light source in Example 2 of this invention. It is a figure for demonstrating the procedure which produces a light source in Example 2 of this invention. It is a graph which shows the emission spectrum obtained from the light source produced in Example 2 of this invention. It is a figure which shows the layer structure of the light source produced in Example 3 of this invention. It is a figure for demonstrating the drive condition of the light source of Example 3 of this invention. It is a figure for demonstrating the drive condition of the light source of Example 3 of this invention. It is a graph which shows the emission spectrum obtained from the light source produced in Example 3 of this invention. It is (a) perspective view (b) top view for demonstrating the light source produced in Example 4 of this invention. It is a graph for demonstrating Example 5 of this invention.

  A light source according to an embodiment of the present invention will be described with reference to FIG. The contents described here are contents common to the examples of the following embodiments.

  The light source according to the embodiment of the present invention includes an SLD 103 having one or more light emitting regions 110 (FIG. 1 shows two light emitting regions) and an emission spectrum conversion region 102, and one or more light emitting devices. The control unit 104 controls the current injected into the region 110 and the emission spectrum conversion region 102. Then, the light emitted from one first light emitting region 111 of the one or more light emitting regions 110 and emitted from the first light emitting region 111 and the light L1 passing through the light emission spectrum conversion region 102. Light L2 that does not pass through the emission spectrum conversion region 102, or one of the one or more emission regions 110 that is emitted from the second emission region 112 different from the first emission region 111, and does not pass through the emission spectrum conversion region 102 The light L3 is configured to be combined. Further, the control unit 104 controls the current injected into the emission spectrum conversion region 102 and the one or more light emission regions 110.

  The light emitted from the first light emitting region 111 passes through the light emission spectrum conversion region 102, so that the short wavelength component of the light emission spectrum is absorbed, but not all the long wavelength component is absorbed. Then, the light that has passed through the emission spectrum conversion region 102 becomes light having a long-wavelength component that is the same as or higher in intensity than the light emitted from the first light emission region 111. Furthermore, the light that has passed through the emission spectrum conversion region 102 is not included in the emission spectrum before passing through, includes a component in a longer wavelength region, or has a weak emission intensity before passing through. In the wavelength region, the emission intensity is increased. Therefore, the light emitted from the light source according to the present embodiment has an emission spectrum having a wide full width at half maximum.

  In addition, as in Embodiments 3 to 5, when light that has passed through the emission spectrum conversion region is incident on another emission region, even if the intensity of the light emitted from the emission spectrum conversion region is small, the light Amplified in another emission region. For example, light that is emitted from the first light emitting region 111, passes through the light emission spectrum conversion region 102, and further passes through the second light emitting region 112, so that light in which light in the long wavelength region is amplified can be emitted. .

  On the other hand, a short wavelength component remains in the emission spectrum of light emitted from the first emission region 111 and not passing through the emission spectrum conversion region 102. Similarly, a short wavelength component remains in the emission spectrum of light emitted from the second emission region 112 and not passing through the emission spectrum conversion region. Therefore, by combining the light L1 and the light L2 or combining the light L1 and the light L3, an emission spectrum having a full width at half maximum larger than that of the light emitted from the first light emitting region 101 is obtained. A light source that emits light can be realized.

  Note that in this specification, a super luminescent diode (SLD) is a kind of light-emitting element, and exhibits an intermediate property between a laser and a light-emitting diode (Light Emitting Diode, LED). Specifically, when the current injected into each of the SLDs is increased, the light output intensity does not change linearly as in the LED, and the slope of the linear change with respect to the threshold current as in the laser It does not show the behavior of changing, and typically shows a change proportional to the square of the injected current amount. Further, the half width of the emission spectrum of the SLD is, for example, 10 nm or more, which is larger than the laser and smaller than the LED.

(Light emitting area)
In the embodiment of the present invention, the light emitting region is a region including an active layer that emits light having a wavelength width.

(Emission spectrum conversion region)
In the embodiment of the present invention, the emission spectrum conversion region is a region where the wavelength and intensity of light guided through the region changes. Specifically, it is a region where a current density smaller than the current density of the light emitting region is injected in the SLD, or an active layer region where no current is injected.

  Further, the amount of conversion of light wavelength and intensity varies depending on the current density injected into the emission spectrum conversion region.

  The emission spectrum conversion region is preferably the same active layer as the light emission region.

  A normal SLD may have a region adjacent to the light emitting region where current injection is not performed. In this case, it is used to absorb light so as to suppress reflection of light in order to suppress laser oscillation. In the present embodiment, a wide spectrum full width at half maximum is obtained by positively using the light guided through the emission spectrum conversion region as the emitted light.

  Hereinafter, the light source according to the embodiment of the present invention will be described in detail with specific examples.

(Active layer)
The quantum well structure suitable for the active layer varies depending on the wavelength of light emission. The emission wavelength of the quantum well structure is determined by the material of the well layer and the barrier layer and the thickness of the well layer. Hereinafter, as an example of a quantum well suitable for the light emission wavelength of the active layer, the light emission wavelength of the ground level of the quantum well will be described as an axis.

For example, Al _x Ga _(1-x) As having an Al composition x of 0 to 0.15 is suitable for the well layer in order to locate the ground level emission in the range of 800 nm to 850 nm. The barrier layer is preferably made of AlGaAs having a higher Al composition. The thickness of the quantum well layer at this time is preferably 5 nm to 10 nm. However, since the emission wavelength of the ground level is determined by the thickness of the well layer and the material constituting the well layer, it can also be realized by using a material with a wavelength shorter than that of 5 nm and a correspondingly small band gap.

In _x Ga _(1-x) As having an In composition of 0 to 0.1 can be used in order to locate the emission of the ground level in the wavelength range of 850 nm to 900 nm. As the material of the barrier layer, GaAs or AlGaAs is preferably used. The thickness of the well layer is preferably 5 nm to 10 nm. However, since the thickness is determined by the thickness of the well layer and the material constituting the well layer, the thickness can be made shorter than 5 nm, and a material having a wavelength with a short band gap can be used.

  Further, even in the same 800 nm to 900 nm band, other materials can be used as long as the material emits light in this wavelength band. For example, a quantum well structure may be realized by using GaInAsP for the well layer and the above idea.

  Similarly, in other wavelength bands, a well layer that emits light in each wavelength band and a material having a wider band gap are used for the barrier layer, and a suitable active layer is realized by adjusting the width of the well layer. it can. For example, in the 980 nm band, InGaAs having an In composition of about 0.2 is suitable for the well layer, and in the case of 1550 nm, InGaAs having an In composition of about 0.68 that lattice matches with the InP substrate is preferably used. Can do.

  It is preferable to use one or more of the above quantum well structures as the active layer of the SLD. When a plurality of quantum well layers are used, light can be emitted with a wider wavelength by using a quantum well structure having a plurality of different emission wavelengths.

  In the above, the quantum well structure was used for the active layer. The quantum well structure is suitable for SLD because of its gain characteristics and ease of manufacturing. However, the active layer structure used for SLD is not limited to the quantum well structure. For example, an active layer with a so-called bulk structure, a quantum wire, or an active layer with a quantum dot structure having a thickness that can reduce the quantum effect may be used.

  In the light source according to the present embodiment, the control unit includes the light emission spectrum conversion region and the first light emission region so that the current density of the light emission spectrum conversion region is 10% or less of the current density of the first light emission region. It is preferable to control the current to be injected.

In the light source according to the present embodiment, the control unit preferably controls the current injected into the emission spectrum conversion region so that the current density in the emission spectrum conversion region is 0 kA / cm ² or more and ² kA / cm ² or less. .

In the light source according to the present embodiment, it is more preferable that the control unit controls the current injected into the emission spectrum conversion region so that the current density of the emission spectrum conversion region is 0 kA / cm ² .

Embodiment 1 (two SLDs)
The light source according to Embodiment 1 will be described with reference to FIG. FIG. 2A is a perspective view schematically showing the light source according to this embodiment, and FIG. 2B is a plan view of FIG. 2A viewed from the direction of the black arrow A1.

  In this embodiment, the SLD is composed of two SLDs, a first SLD 210 and a second SLD 220 formed on the same substrate.

  The first SLD 210 has a first light emission region 211 and an absorption region 215, and the second SLD 220 has an emission spectrum conversion region 222 and a second light emission region 221.

  In the first SLD 210, current is injected into the first light emitting region 211, and outgoing light is extracted from the outgoing end face of the first light emitting region 211. In the second SLD 220, current is injected into the second light emission region 221, and the emitted light is extracted from the emission end face of the emission spectrum conversion region 222 through the emission spectrum conversion region 222.

  Each light is multiplexed using the optical fiber 230.

  Note that the first light emitting region 211, the second light emitting region 221, the light emission spectrum conversion region 222, and the light emission spectrum conversion region 215 have the same active layer 240.

  The first SLD 210 and the second SLD 220 have a ridge waveguide structure, and the first light emitting region 211 and the absorption region 215, and the light emission spectrum conversion region 222 and the second light emitting region 221 are waveguides on the same axis. Is formed.

  FIG. 3A (a cross-sectional view of FIG. 2A viewed from the direction indicated by the black arrow A2) is shown to show the layer structure of the structure of the light source according to the present embodiment. FIG. 3B is a cross-sectional view as viewed from a direction different from that of FIG. 3A by 90 degrees. In FIG. 3B, the insulating layer 360 and the like are partially omitted. In addition, multilayer dielectric films may be added to the end surfaces of the first SLD 210 and the second SLD 220 in order to control the reflectance. In FIG. 3, 380 is a lower electrode, 310 is a substrate, 320 is a lower cladding layer, 240 is an active layer, 340 is an upper cladding layer, 350 is a contact layer, 360 is an insulating layer, and 370 is an upper electrode.

  Although the manufacturing method of the light source is specifically shown in the first embodiment, the dimensions of each component of the light source, each manufacturing process, and various parameters are not limited to the first embodiment.

  In the present embodiment, in an SLD having a light emitting region for performing current injection and a light emission spectrum conversion region, it is possible to obtain broadband spectral characteristics by guiding light generated in the light emission region through the light emission spectrum conversion region. Is.

  Here, if the length of the emission spectrum conversion region is too short, the spectrum shape will hardly change even if the light generated in the emission region is guided through the emission spectrum conversion region, or the intensity will be slightly reduced. The effect of the present invention cannot be obtained. If the emission spectrum conversion region is too long, most of the light generated in the light emission region is absorbed. Therefore, even if the light is combined, the effect is thin and does not contribute to the broadening of the spectrum.

  The length of the emission spectrum conversion region is preferably shorter than the length at which the light on the short wavelength side is absorbed more than the wavelength located at the peak intensity of the light that is emitted directly from the light emitting region.

  Moreover, it is preferable that the peak intensity of light emitted from the emission end face of the emission spectrum conversion region has an intensity of ¼ or more as compared with the peak intensity of light emitted as it is from the emission region. Furthermore, if it is 1/2 or more, it is preferable because the strength is sufficient to widen the full width at half maximum.

  Moreover, it is preferable that the wavelength located at the peak intensity of the light emitted from the emission spectrum conversion region emission end face is longer than the wavelength located at the peak intensity of the light emitted from the light emission region as it is. Furthermore, it is preferable that the wavelength is on the longer wavelength side than the wavelength positioned on the longer wavelength side that is half the peak intensity of the light that is emitted as it is from the light emitting region.

  Here, a preferable range of the length L of the emission spectrum conversion region is shown below.

  P1 (λ) is the light intensity of the light emitted from the light emitting region emitting end face when current in the light emitting region is injected, and the light emitted from the light emitting spectrum converting region emitting end face is guided through the light emitting spectrum converting region. P2 (λ) is the light intensity of light generated when a current in the light emitting region is injected, and P3 (λ) is the light intensity of light emitted from the light emission spectrum conversion region exit end face through the light emission spectrum conversion region. λ). The wavelength located at the peak intensity of P1 is λ1, the wavelength located at the peak intensity of P3 is λ3, and the absorption coefficient at each wavelength is α (λ). The combined light used in the present invention is P1 (λ) + P3 (λ). Further, P3 (λ) = P2 (λ) · exp (−α (λ) · L).

Since the light on the short wavelength side is absorbed to some extent, the lengths at which the intensities P3 (λ1) and P3 (λ2) at λ1 and λ2 of P3 (λ) are the same value,
P2 (λ1) · exp (−α (λ1) · L) = P2 (λ2) · exp (−α (λ2) · L)
That is, it is preferable that L is longer than L = ln {P2 (λ1) / P2 (λ2)} / {α (λ1) −α (λ2)}.

In order to produce a certain effect when combined, the length that the peak intensity of P3 has an intensity of 1/4 or more compared to the peak intensity of P1,
1/4 · P1 (λ1) <P2 (λ2) · exp (−α (λ2) · L)
That is, L <ln {4 · P2 (λ2) / P1 (λ1)} / α (λ2)
L is preferably satisfied.

  Moreover, it is preferable that the current passed through the light emitting region in order to obtain P1 (λ) has such a high current density that the spectrum on the short wavelength side emits light. It is preferable that the current passed through the light emitting region to obtain P2 (λ) has such a high current density that a peak intensity equivalent to the peak intensity of P1 can be obtained.

  Unlike the emission spectrum conversion region 222, the absorption region 215 is installed on the side opposite to the emission end face of the first emission region 211, that is, the end face from which the emission light of the first SLD 210 is extracted, and serves to suppress reflection. It is what. Although it is not essential to provide the absorption region 215 as the essence of the present invention, it is provided in this embodiment because it is simple in forming the element and contributes to suppressing reflection. For the same purpose, an absorption region may be provided in a portion adjacent to the second light emitting region 221 of the second SLD 220 on the opposite side to the light emission spectrum conversion region 222.

  In this embodiment, the first SLD 210 uses light emitted from the emission end face of the first light emitting region 211, and the second SLD 220 uses light emitted from the emission end face of the emission spectrum conversion region 222. The light emitted from the end face of the second light emitting region 221 may be used by the end face of 215 or the second SLD 220. These may be combined to be used as a higher-output, wider-band SLD, or used as monitor light for each SLD. In that case, the absorption region 215 can be used not only to suppress reflection but also to contribute to a broad band like the emission spectrum conversion region 222.

  The length of the emission region and emission spectrum conversion region of each SLD and the amount of injected current may be appropriately changed, and an arbitrary spectrum shape can be obtained by combining them under appropriate conditions. A reverse bias may be applied to the emission spectrum conversion region as well as a configuration in which current is injected or not injected.

  Note that the above formation method, semiconductor material, electrode material, dielectric material, and the like are not limited to those disclosed in the embodiment, and other methods and materials may be used as long as they do not depart from the spirit of the present invention. Is also possible.

  For example, a p-type GaAs substrate may be used as the substrate, in which case the conductivity type of each semiconductor layer is changed accordingly.

  As the active layer, an asymmetric multiple quantum well having a different well width is used, but the present invention is not limited to this. Instead of quantum wells having different well widths, asymmetric multiple quantum wells having different composition ratios may be used, or both the well width and composition ratio may be changed. The number of quantum wells is not limited to four, and two or three quantum wells may be used.

  Further, the material is not limited to this, and a light emitting material such as GaAs, GaInP, AlGaInN, AlGaInAsP, and AlGaAsSb may be used.

  In Example 1 below, the ridge width is 4 μm, but the present invention is not limited to this and may be changed as appropriate.

  Each SLD has a structure in which a ridge is used and the ridge is inclined. However, any structure that operates as an SLD may be used. For example, a structure that suppresses reflection with a window structure without using an inclined ridge may be used.

  Further, when no voltage is applied as in this case, a configuration may be adopted in which current injection cannot be performed by removing the insulating film above the ridge.

  Here, multiplexing is performed using an optical fiber as a multiplexing unit, but other multiplexing methods may be used as long as the outputs from the respective SLDs can be combined.

  Although the light emitting region is composed of one electrode, the light emitting region may be composed of a plurality of electrodes and driven by injecting current into each of the electrodes. Alternatively, the emission spectrum conversion region may be configured by a plurality of electrodes, and may be driven by being divided into a portion where no current flows and a portion where a reverse bias is applied.

  Although two SLDs are used, it may be configured using three or more SLDs. In that case, the lengths of the emission regions and the emission spectrum conversion regions of the respective SLDs may all be different, and the number of SLDs that use the light emitted from the end face of the emission spectrum conversion region may be two or one.

(Example of combining unit monolithic)
Another example of the light source according to the embodiment of the present invention will be described with reference to FIG. FIG. 4A is a perspective view schematically showing the light source according to the present embodiment, and FIG. 4B is a plan view of FIG. 4A viewed from the direction of the black arrow.

  In this example, there are two SLDs, the first SLD 410 and the second SLD 420, the light emitted from the light emission end face of the first light emission region 411 of the first SLD 410, and the light emission end face of the light emission spectrum conversion region 422 of the second SLD 420. The combining portion 430 for combining the emitted light is formed monolithically and has the same active layer 440.

  In this embodiment, an n-type clad layer, an active layer, a p-type clad layer, and a contact layer are stacked on an n-type substrate.

  The ridge portion and the combining portion 430 of the first SLD 410 and the second SLD 420 are formed using a general semiconductor lithography method and semiconductor etching.

  The first light emitting region 411 of the first SLD 410, the light emission spectrum conversion region 415 and the second light emission region 421 of the second SLD 420, the light emission spectrum conversion region 422, and the multiplexing unit 430 can be independently driven by current. Each is formed with an upper electrode. The electrodes are electrically separated by removing the Ti / Au and GaAs contact layers of the upper electrode using, for example, photolithography and wet etching.

  In this embodiment, not only the first SLD 410 and the second SLD 420 but also an electrode is provided on the multiplexing unit 430 so that current injection is possible. By injecting a certain amount of current into the multiplexing unit 430, absorption of light guided by the multiplexing unit 430 can be suppressed.

  In the description of the following embodiment, points different from the first embodiment will be described, and the description of common points will be omitted. For example, since the layer configuration of the light source according to the following embodiment is the same as that of FIG. 3 shown in the first embodiment, description and description on the drawing are omitted.

(Embodiment 2) (One SLD)
A second embodiment of the present invention will be described with reference to FIG. FIG. 5A is a perspective view schematically showing the light source according to the present embodiment, and FIG. 5B is a plan view of FIG. 5A viewed from the direction of the black arrow.

  The light source according to the present embodiment is composed of one SLD 510. The SLD 510 has a light emission region 511 and a light emission spectrum conversion region 512, injects current into the light emission region 511, takes out the emitted light from the emission end surface of the light emission region 511 and the emission end surface of the light emission spectrum conversion region 512, and combines them. .

  In the first embodiment, the lengths of the first SLD 210 and the second SLD 220 of the first SLD 210 and the second SLD 220 are equal to each other, and the absorption region 215 and the emission spectrum conversion region 222 are equal in length. The configuration of this embodiment is possible when the current injected into each light emitting region is the same. In this configuration, the power supply can be reduced, and a simpler configuration can be taken.

  Further, in order to obtain a large output, a plurality of the present configuration SLDs may be arranged in parallel. At that time, if the same power source is used, it is possible to drive with one power source.

(Embodiment 3)
Embodiment 3 of the present invention will be described with reference to FIG. FIG. 6A is a perspective view schematically showing the light source according to the present embodiment, FIG. 6B is a view of FIG. 6A viewed from the point X, and FIG. It is the figure seen from the Y point. As shown in FIG. 6, 600 is a semiconductor laminated film (including a substrate), 602 is an active layer, 604 is an insulating film, 606 is an upper electrode, 608 lower electrode, 610 is a first light emitting region, and 612 is a second light emitting. An area 614 is an emission spectrum conversion area, and 616 is a first end face.

  With this configuration, when the light generated in the light emission region is guided through the light emission spectrum conversion region, the short wavelength component of the light spectrum generated in the light emission region is absorbed, and the long wavelength component is mainly used. Light having a spectrum is emitted. Comparing the light intensity of the long wavelength component of the light emitted through the emission spectrum conversion region and the light generated in the emission region directly emitted from the emission region without being guided through the emission spectrum conversion region The light emitted through the emission spectrum conversion region has a longer wavelength component with higher intensity. The light with the short wavelength component absorbed and the intensity of the long wavelength component increased is guided to a light emitting region different from the light emitting region where the light was originally generated, and current is injected into the light emitting region, thereby optical amplification. Thus, light having a spectrum mainly composed of a long wavelength component with increased intensity is emitted. Light is also generated in the amplified light emitting region, and the light has a spectrum mainly composed of short wavelengths. Compared with the light emitted and emitted in the light emitting region by simultaneously emitting light having a spectrum mainly composed of short wavelength components and light having a spectrum mainly composed of long wavelength components from the same end face Thus, it is possible to obtain light having a broad spectrum full width at half maximum.

  In addition, when the waveguide in the emission spectrum conversion region is short, the light generated in the emission region is not sufficiently absorbed even when guided through the emission spectrum conversion region (compared to the case where the length of the emission spectrum conversion region is appropriate, Absorption on the short wavelength side is insufficient and the long wavelength component is not the main component), and the effect of broadening the spectrum is small. On the other hand, if the waveguide in the emission spectrum conversion region is too long, the light generated in the emission region is absorbed when guided through the emission spectrum conversion region, and the effect of the present invention cannot be obtained. Does not contribute.

  The length of the emission spectrum conversion region is such that the light generated in the second (first) emission region is guided in the first (second) emission region after being guided in the wavelength conversion region. The peak wavelength λ1 of the spectrum when emitted from the (second) end face is that of the spectrum when the light generated in the first (second) emission region is emitted from the first (second) end face. A configuration in which the wavelength is longer than the peak wavelength λ2 (λ1 <λ2) is preferable.

  As described above, according to the configuration of the present embodiment, an SLD having a broadband and high output spectrum can be realized easily and inexpensively.

  In the present embodiment, the upper electrode 606 is not formed in the emission spectrum conversion region 614, but the present invention is not limited to this, and the upper electrode 606 may be formed. In the case of forming the upper electrode 606, current injection is not performed, or reverse bias is injected, or the like, which can be selected as appropriate depending on the configuration (the length of each region). In the present embodiment, the upper electrode 606 formed in the light emitting region is a single one, but the present invention is not limited to this, and a plurality of upper electrodes may be formed. In addition, when the upper electrode is formed in the emission spectrum conversion region, a single or a plurality of upper electrodes may be formed. In this embodiment, the active layer 602 has an asymmetric quantum well structure with different well widths, but is not limited to this. An asymmetric quantum well structure with different composition ratios or an asymmetric structure in which the well width and the composition ratio are modulated simultaneously. It may be a quantum well structure. Further, the number of quantum wells is not limited to four. Moreover, a single quantum well structure or a normal multiple quantum well structure may be used. Further, the material is not limited to InGaAs.

  In Example 2 below, the length of the first light emitting region 610 is 0.2 mm, the length of the second light emitting region 612 is 0.25 mm, and the length of the light emission spectrum conversion region 614 is 0.25 mm. However, it is not limited to this, and may be changed as appropriate. Further, the ridge width of 3 μm and the ridge height of 0.8 μm are not limited thereto. The length of each light emitting region, the light emission spectrum conversion region, and the amount of injected current may be appropriately changed, and an arbitrary spectrum shape can be obtained by combining an appropriate length and the amount of injected current.

  Further, the present invention is not limited to the technique (apparatus) used for the MOCVD crystal growth technique, lithography, etching, ashing, and vapor deposition shown in Example 2 below, or the technique (apparatus) described, and similar effects can be obtained. Any method (apparatus) may be used.

(Embodiment 4)
Embodiment 4 of the present invention will be described with reference to FIG. FIG. 7A is a perspective view schematically showing the light source according to the present embodiment, and FIG. 7B is a view seen from the point X in FIG. 7A. This embodiment is an example of a super luminescent diode (SLD) that uses light emitted from two end faces of an element as a signal. The length and the injection current amount of the first light emission region 710, the second light emission region 712, and the light emission spectrum conversion region 714 are set optimally (for example, the first light emission region 710 and the second light emission region 712 Emission light having a broadband spectrum is obtained from each of the first end surface 716 and the second end surface 718 by setting the lengths equal and setting the length of the light emission spectrum conversion region 714 to be longer than the two light emission regions). It becomes possible to obtain a broadband and high-power SLD by combining the emitted lights using an optical fiber (not shown). Further, one of the outgoing lights from both end faces may be used as monitoring light. In FIG. 7 illustrating the configuration of the present embodiment, the upper electrode 706 is not formed in the emission spectrum conversion region 714, but the present invention is not limited to this, and the upper electrode 706 may be formed. In the case of forming the upper electrode 706, current injection is not performed, or reverse bias is injected, or the like, which can be appropriately selected depending on the configuration (the length of each region, etc.). Further, in this embodiment, the multiplexing by the optical fiber is used as the multiplexing means. However, the present invention is not limited to this, and other multiplexing methods can be used as long as the emitted light from both end faces can be multiplexed. There may be.

(Embodiment 5)
In the present embodiment, in an SLD having a light emitting region for injecting current, a light emitting spectrum conversion region, and a reflection part on one end face, light generated in the light emitting region is guided through the light emission spectrum converting region and the light emitting region. This makes it possible to obtain a broadband spectral characteristic.

  The light source according to this embodiment will be described with reference to FIG. FIG. 8A is a perspective view schematically showing a light source according to the present embodiment, and FIG. 8B is a plan view of FIG. 8A viewed from the direction of a black arrow.

  The light source according to the present embodiment has a ridge waveguide structure. The light emitting region 801 adjacent to the light emitting end surface, the light emission spectrum converting region 803 adjacent to the light emitting region, and the reflective film 805 provided on the end surface opposite to the light emitting side. Consists of. By doing so, the light emitted from the light emitting region as it is and the light once guided through the light emission spectrum conversion region from the light emitting region can be emitted from the same emission end face 806. Therefore, it is possible to easily obtain light having a simple structure and a wide full width at half maximum.

  Note that the above formation method, semiconductor material, electrode material, dielectric material, and the like are not limited to those disclosed in the embodiment, and other methods and materials may be used as long as they do not depart from the spirit of the present embodiment. It is also possible. For example, the substrate may be a p-type GaAs substrate, in which case the conductivity type of each semiconductor layer is changed accordingly.

  The active layer employs a single quantum well structure, but may have a multiple quantum well structure or an asymmetric multiple quantum well structure with different well widths and composition ratios.

  Further, the material is not limited to this, and a light emitting material such as GaAs, GaInP, AlGaInN, AlGaInAsP, and AlGaAsSb may be used.

  Although the ridge width is 4 μm, it is not limited to this and may be changed as appropriate.

  Each SLD has a structure in which a ridge slope is provided by using a ridge portion. However, any structure may be used as long as it operates as an SLD. For example, the ridge may not be provided and may be used as a substitute for a highly reflective film.

  The light exit end is determined to be adjacent to the light emitting region, but an absorption region (window region) where no voltage is applied between the light emitting region and the light exit end in order to suppress reflection of light at the light exit end. It may be provided.

  Regarding the emission spectrum conversion region, the absorption characteristic may be changed by applying a reverse bias voltage. Further, when no voltage is applied to the emission spectrum conversion region as in this embodiment, a configuration may be adopted in which current injection cannot be performed by removing the insulating film above the ridge.

  Although the light emitting region is composed of one electrode, the light emitting region may be composed of a plurality of electrodes and driven by injecting current into each of the electrodes. Alternatively, the emission spectrum conversion region may be configured by a plurality of electrodes, and may be driven by being divided into a portion where no current flows and a portion where a reverse bias is applied.

  Here, if the length of the light emission spectrum conversion region is too short, the spectral shape of the light after being guided hardly changes, so that the effect of the light source cannot be sufficiently obtained in this embodiment. On the other hand, if the emission spectrum conversion region is too long, the intensity of the light after being guided is too weak, and the effect of the present embodiment cannot be sufficiently obtained. Here, a preferable range as the length L of the emission spectrum conversion region is shown below.

The peak wavelength in the spectrum of the light generated in the emission region and emitted as it is is λ ₁ , the peak wavelength of the spectrum after being guided through the emission spectrum conversion region is λ ₂ , and the absorption coefficient at λ ₁ is α ₁ , The absorption coefficient at λ ₂ is α ₂ . Further, the intensity of light at the wavelength λ ₁ immediately before being guided through the emission spectrum conversion region is P ₁ , the intensity at λ ₂ is P ₂ , the emission spectrum conversion region is guided, and the active layer region is guided again. Then, the intensity at the wavelength λ ₁ of the amplified light is P ₁ ′, and the intensity at λ ₂ is P ₂ ′. Here, the amplification factor of light at λ ₁ is A ₁ , and the amplification factor of light at λ ₂ is A ₂ .

First, the lower limit value of L will be described. The present invention is characterized in that the peak wavelength shifts to the longer wavelength side when guided through the emission spectrum conversion region. Since this effect appears when λ ₁ ≦ λ ₂ , the lower limit value of L is when λ ₁ = λ ₂ ,

It becomes.

Next, the upper limit value of L will be described. In order to sufficiently obtain the effects of the present invention, it is necessary that the light guided through the emission spectrum conversion region and further guided through the light emission region has a certain size. This size is set to P _min . If P ₂ is _P 1/2 or more, the effect is obtained _{for P 2} 'to extending the band in the order of _P 1/4. If P ₂ is less than _{P 1/2, P} 2 'is required _P 1/2 or more in order to spread the full width at half maximum. Therefore, the upper limit of L is

It becomes.

(Embodiment 6)
In this embodiment, an optical coherence tomography (OCT) apparatus using the light source according to the first to fifth embodiments will be described with reference to FIG. The OCT apparatus according to the present embodiment branches into the light source described above, irradiation light that irradiates the object with light from the light source, and reference light, and interference caused by reflected light of the light irradiated on the object and the reference light Information on the object based on the intensity of the interference light, an interference optical system that generates light, a wavelength dispersion unit that wavelength-disperses the interference light, a light detection unit that receives the wavelength-dispersed interference light, and And an information acquisition unit to be acquired.

  The OCT apparatus according to the present embodiment includes at least a light source 901, an interference optical system 902, a wavelength dispersion unit 963, a light detection unit 964, and an information acquisition unit 970. The light source 901 is a light source according to the first to fifth embodiments. It is.

  The light emitted from the light source 901 passes through the interference optical system 902 and is output as interference light having information on the object 950 to be measured. The interference light applied to the wavelength dispersion unit 963 is received in such a manner that light of different wavelengths is applied to different positions of the light detection unit 964. The information acquisition unit 970 acquires information on the object 950 (for example, information on a tomographic image) from the information on the intensity of light received by the light detection unit 964.

  Next, details of the OCT apparatus according to the present embodiment will be described with reference to an example.

  The OCT apparatus shown in FIG. 9 irradiates light to a light output unit 900, a light dividing unit 910 that divides light emitted from the light output unit 900 into reference light and measurement light, a reference light reflection unit 930, and a measurement object 950. A measurement unit 920 including an irradiation optical system 940, an interference unit 915 for causing the reflected reference light and the reflected measurement light to interfere, a light detection optical system 960 for detecting the interference light obtained by the interference unit, and a light detection optical system 960 The information acquisition part 970 which acquires the information regarding a tomogram based on the light detected by (3) and the display part 980 which displays a tomogram are comprised.

  The light output unit 900 is demultiplexed into reference light and measurement light by the light dividing unit 910 via an optical fiber, and part of the demultiplexed light enters the reference light reflecting unit 930. Here, the light splitting unit 910 and the interference unit 915 use the same fiber coupler.

  The reference light reflecting section 930 includes collimator lenses 931 and 932 and a reflecting mirror 933, which is reflected by the reflecting mirror 933 and enters the optical fiber again. The measurement light, which is the other light demultiplexed by the light splitting unit 910 from the optical fiber, enters the measurement unit 920. The irradiation optical system 940 of the measuring unit 920 includes collimator lenses 941 and 942 and a reflecting mirror 943 for bending the optical path by 90 °. The irradiation optical system 940 serves to enter the incident light to the measurement object 950 and to couple the reflected light to the optical fiber again.

  The light returned from the reference light reflection unit 930 and the measurement unit 920 passes through the interference unit 915 and enters the light detection optical system 960. The light detection optical system 960 includes collimator lenses 961 and 962, a spectroscope 963, and a line sensor 964 for obtaining spectral information of light dispersed by the spectroscope as the wavelength dispersion unit 963. The spectroscope 963 uses a grating. The light detection optical system 960 is configured to obtain spectral information of light incident thereon.

Example 1
Example 1 is the same as in Example 1 (FIGS. 1, 2, and 3).
an InGaAs asymmetric multiple quantum well in which the well width of each quantum well is modulated using n-Al _0.5 GaAs as the n-type cladding layer 320 and four quantum wells as the active layer 240 on the n-type GaAs substrate 310, p This is a light source in which p-Al _0.5 GaAs is stacked as the mold cladding layer 340 and highly doped p-GaAs is stacked as the contact layer 350.

  The ridge portions of the first SLD 210 and the second SLD 220 are partially removed partway between the contact layer 350 and the p-type cladding layer 340 as shown in FIG.

  After forming the ridge portion, an insulating film 360 and an upper electrode 370 are provided on the upper surface, and a lower electrode 380 is provided on the lower surface of the substrate.

  The upper electrode 370 forms the first light emitting region 211 and the absorption region 215 in the first SLD 210, and forms the second light emitting region 221 and the light emission spectrum conversion region 222 in the second SLD 220 to drive each independently. Separated electrodes were obtained.

SiO ₂ was used for the insulating film 360, Ti / Au was used for the upper electrode 370, and AuGe / Ni / Au was used for the lower electrode 380.

  The element lengths of the first SLD 210 and the second SLD 220 are 0.2 mm for the first emission region 211, 0.25 mm for the emission spectrum conversion region 215, 0.2 mm for the emission spectrum conversion region 222, and the second emission region 221. Is 0.25 mm. The electrode separation width of each region was about several um, and the ridge width was 4 um.

  In order to prevent reflection at the ridge end face, the ridge portion was inclined by 7 degrees with respect to the normal of the ridge end face and the longitudinal direction of the ridge.

  Next, a procedure for manufacturing a light source in Example 1 is shown below.

  First, a semiconductor layer, that is, an n-type cladding layer 320, an active layer 240, a p-type cladding layer 340, and a contact layer 350 are sequentially grown on the GaAs substrate 310 by using, for example, a MOCVD (Metal Organic Chemical Vapor Deposition) method. .

A ridge portion was formed on the wafer on which each layer was laminated by using a general semiconductor lithography method and semiconductor etching. After forming SiO ₂ using a sputtering method, a stripe forming mask for forming a ridge was formed using a photoresist using a semiconductor lithography method. Next, the semiconductor other than the stripe formation mask was selectively removed using a dry etching method. At this time, a portion to be removed was partway through the p-type cladding layer 340, and a ridge shape having a depth of 0.8 μm was formed.

Next, a dielectric film, for example, SiO ₂ was formed on the semiconductor surface, and SiO ₂ on the upper portion of the ridge portion was partially removed by photolithography and wet etching. Next, the first light-emitting region 211 and the absorption region 215, and the second light-emitting region 221 and the light-emission spectrum conversion region 222 are formed on the first SLD 210 and the second SLD 220 by using a vacuum deposition method and a lithography method. For this purpose, an upper electrode 370 (Ti / Au) was formed. The electrode separation widths of the first light emitting region 211 and the absorption region 215, and the second light emitting region 221 and the light emission spectrum conversion region 222 are about several um. Further, the contact layer 350 in the electrode separation portion was removed by wet etching.

  Before forming the lower electrode 380, the GaAs substrate 310 was thinned to a thickness of about 100 μm by polishing. And the lower electrode 380 (AuGe / Ni / Au) was formed using the vacuum evaporation method. In order to obtain good electrical characteristics, annealing was performed in a high-temperature nitrogen atmosphere to alloy the electrode and the semiconductor. Finally, a crystal plane was formed on the end face by cleavage, and a dielectric film for adjusting the reflectance was coated on both end faces to complete.

  FIG. 10 shows spectral characteristics obtained by combining the first SLD 210, the second SLD 220, and the two outgoing lights. As shown in FIG. 10, the emission spectrum (SLD 210) of light emitted only from the first emission region 211 has a peak at a short wavelength, but is emitted from the second emission region 221 and guided through the emission spectrum conversion region 222. The emission spectrum of the light (SLD 220) has a peak on the long wavelength side. Also, the two emission spectra have overlapping portions, and when combined, the result is a waveform with a large half width.

  In the first SLD 210, a current of 150 mA is injected into the first light emitting region 211, and outgoing light is extracted from the outgoing end face of the first light emitting region 211. In the second SLD 220, a current of 200 mA is injected into the second light emission region 221, guided through the light emission spectrum conversion region 222, and emitted light is extracted from the emission end face of the light emission spectrum conversion region 222. Note that no current is injected into the absorption region 215 and the emission spectrum conversion region 222.

  Compared to the first SLD 210 that is a normal SLD not guided through the emission spectrum conversion region 222, the second SLD 220 that is guided through the emission spectrum conversion region 222 emits light on the short wavelength side. It can be seen that the spectrum has peak intensity on the long wavelength side. Further, the second SLD 220 has an intensity greater than that of the first SLD 210 on the long wavelength side. Compared to the first SLD 210, the spectrum obtained by combining these can be confirmed to spread on the long wavelength side, and to obtain a wide spectrum full width at half maximum. In the SLD of the same active layer as in this embodiment, it is difficult to obtain such an effect without having an emission spectrum conversion region.

  As in this embodiment, the wavelength located at the peak intensity in the second SLD 220 is longer when located on the long wavelength side than the wavelength located on the long wavelength side that is half the peak intensity of the first SLD 210. The full width at half maximum can be expanded to the wavelength side.

  The second SLD 220 can obtain greater intensity than the first SLD 210 on the long wavelength side, and the peak intensity of the second SLD 220 is not very small compared to the peak intensity of the first SLD 210, for example as shown here It is good to have a strength of 1/4, preferably half or more. In addition, when the peak intensity of the second SLD 220 is too large, there is a possibility that the half width is narrowed. For example, the peak intensity of the second SLD 220 is less than twice the peak intensity of the first SLD 210. Is preferred.

(Example 2)
In this example, the length of the first light emitting region 610 is 0.2 mm, the length of the second light emitting region 612 is 0.25 mm, and the length of the light emission spectrum conversion region 614 in Embodiment 3 (FIG. 6). Was 0.25 mm. By adopting such a configuration, 170 mA is injected into the first light emitting region 610 and 30 mA is injected into the second light emitting region 612 at the same time, thereby emitting light having a broader emission spectrum than the first end surface 616. Can be obtained. In this embodiment, no current is injected into the emission spectrum conversion region 614. Next, a method for manufacturing the SLD of this example will be described.

  FIG. 11 and FIG. 12 are diagrams for explaining a method of manufacturing an SLD in this example.

  First, as shown in FIG. 11A, a semiconductor laminated film 600 including an active layer 602 is sequentially laminated on a substrate using MOCVD crystal growth technology. The active layer 602 of this embodiment has a multiple quantum well structure composed of four quantum wells, and has an InGaAs asymmetric quantum well structure in which the well width of each quantum well is modulated.

  Subsequently, as illustrated in FIG. 11B, a first resist pattern 620 is formed on the semiconductor stacked film 600 by using a lithography technique.

  Next, as shown in FIG. 11C, a ridge structure is formed by dry etching using the first resist pattern 620 as an etching mask. Thereafter, the resist pattern 620 is removed by ashing.

  In this embodiment, the width of the ridge structure is 3 μm and the height is 0.8 μm. Further, the longitudinal direction (waveguide axis) of the ridge structure was formed to be inclined by 7 degrees with respect to the normal of the end face.

  Further, although the resist pattern 620 is used as an etching mask, a dielectric (eg, SiO 2) may be used as an etching mask.

  Next, as shown in FIG. 11D, an insulating film 604 is formed using PECVD technology so as to cover the entire region. As a material of the insulating film 604, silicon oxide, silicon nitride, or the like can be used.

  Next, as shown in FIG. 11E, the second active region 610 and the second active region 612 are formed by using a lithography technique so that only the upper part of the ridge is exposed. A resist pattern 622 is formed.

  Next, as shown in FIG. 12A, insulation of the upper portion of the ridge in the region where the first active region 610 and the second active region 612 are formed by wet etching using buffered hydrofluoric acid (BHF). The film 604 is removed. Thereafter, the second resist pattern 622 is removed.

  Next, as shown in FIG. 12B, a third resist pattern 624 is formed so as to cover the region where the emission spectrum conversion region is formed. This resist pattern determines the lengths of the first active region 610, the second active region 612, and the emission spectrum conversion region 614.

  Next, as shown in FIG. 12C, a Ti / Au layer is deposited on the surface using a metal deposition technique. Thereafter, the upper electrode 606 is formed by a lift-off technique so as to exclude the region that forms the emission spectrum conversion region.

  Next, in the step shown in FIG. 12E, AuGe / Ni / Au is vapor-deposited on the back surface side of the semiconductor multilayer film (including the substrate) 600 by using a metal vapor deposition technique to form the lower electrode 608. Subsequently, the first end face 616 and the second end face 618 are crystallized by cleavage to divide the element, and then a dielectric film for adjusting the reflectance of the end face is coated on both end faces. Completion.

  FIG. 13 shows the emission spectrum of the emitted light from the SLD described in this example. A broken line is an emission spectrum when light generated by current injection only into the first light emitting region 610 is emitted from the first end face 616. The solid line indicates that light generated by injecting current into the first light emitting region 610 is emitted from the first end face 616, and at the same time, the light generated by injecting into the second light emitting region 612 is converted into the emission spectrum conversion region 614. It is an emission spectrum when the first light emitting region 610 is guided after being guided and emitted from the first end face 616.

(Example 3)
Example 3 shows a specific example of the light source in the fifth embodiment (FIG. 8).

FIG. 14 is a cross-sectional view showing the layer structure of the light source according to this example. In FIG. 15, the insulating film 808 and the like are partially omitted. In this example, an n-type GaAs substrate 813, an n-type Al _0.5 GaAs as an n-type cladding layer 812, an InGaAs single quantum well using one quantum well as an active layer 811, and a p-type cladding layer 810. P-Al _0.5 GaAs and a highly doped p-GaAs as the contact layer 809 are stacked. The ridge portion is partially removed partway between the contact layer 809 and the p-type cladding layer 810. After forming the ridge portion, an insulating film 808 and an upper electrode 807 are provided on the upper surface, and a lower electrode 814 is provided on the lower surface of the substrate. The upper electrode 807 is an electrode separated for independent driving. SiO ₂ is used for the insulating film 808, Ti / Au is used for the upper electrode 807, and AuGe / Ni / Au is used for the lower electrode 814.

  The element length is 0.5 mm in the active region 801 and 0.125 mm in the emission spectrum conversion region 803. The electrode separation width of each region is about several um. The ridge width is 4 um. The ridge portion is inclined by 7 degrees with respect to the normal of the ridge end surface and the longitudinal direction of the ridge in order to prevent reflection at the ridge end surface. Further, a multilayer dielectric film may be added to the end face in order to control the reflectance.

  Next, the actual device manufacturing procedure is shown below. First, an n-type cladding layer 812, an active layer 811, a p-type cladding layer 810, and a contact layer 809 are sequentially grown on a GaAs substrate 813 by using, for example, a MOCVD (Metal Organic Chemical Vapor Deposition) method.

A ridge portion is formed on the wafer in which each layer is laminated by using a general semiconductor lithography method and semiconductor etching. For example, after forming a dielectric film and SiO ₂ using a sputtering method, a stripe forming mask for forming a ridge is formed using a photoresist using a semiconductor lithography method. Therefore, the dry etching method is used to selectively remove portions of the semiconductor other than the stripe formation mask. At this time, a portion to be removed is partway through the p-type cladding layer 810, and a ridge shape having a depth of, for example, 0.8 μm is formed.

Next, a dielectric film, for example, SiO ₂ is formed on the semiconductor surface, and the SiO ₂ on the ridge portion is partially removed by photolithography and wet etching. Thereafter, the upper electrode 807 is formed using a vacuum deposition method and a lithography method. The upper electrode 807 is, for example, Ti / Au. Further, the contact layer 809 in the electrode separation portion is removed by wet etching.

  Before forming the lower electrode 114, the GaAs substrate 813 is thinned to a thickness of about 100 μm by polishing. Then, the lower electrode 814 is formed using a vacuum evaporation method. The lower electrode 114 is, for example, AuGe / Ni / Au. In order to obtain good electrical characteristics, annealing is performed in a high-temperature nitrogen atmosphere to alloy the electrode and the semiconductor.

  Finally, a crystal plane is formed on the end face by cleavage, and a highly reflective film 805 is coated on the end face opposite to the light emitting side. The reflectance is 99% by attaching a dielectric DBR as a highly reflective film.

  Then, the measurement result in a present Example is shown. This measurement is performed in a form equivalent to the present embodiment as shown in the perspective view shown in FIG. 15 and the plan view shown in FIG. The emission spectrum conversion region 1503 is sandwiched from both sides by the same length region where current can be injected as shown in the figure, and when the current injection is performed only in the region in contact with the light emitting end 1506, both of the driving conditions (1) The driving condition (2) is when the current is injected. In the driving condition (1), this corresponds to the case where the light generated from the active region 801 is emitted as it is in the third embodiment. This corresponds to the case where light is guided through the active region 801 and emitted. Note that the lengths of the two active regions 1501 are both 0.5 mm, and a current of 250 mA is injected into one or both. The length of the emission spectrum conversion region 1503 is 0.25 mm.

  The emission spectra of the driving conditions (1) and (2) are shown in FIG. From this figure, it can be seen that the spectrum under the driving condition (2) has a broad spectrum full width at half maximum as compared with the spectrum under the driving condition (1). This is because another peak appears in the vicinity of 870 nm on the longer wavelength side than the peak wavelength 840 nm in the driving condition (1) by guiding through the emission spectrum conversion region 803.

  In the SLD of the same active layer as in this embodiment, it is difficult to obtain such an effect without having an emission spectrum conversion region. Since the light emission on the short wavelength side becomes remarkable when the current density is increased, the present invention that can enhance the light emission on the long wavelength side while maintaining the same output is particularly effective.

  In order to obtain a wide spectrum full width at half maximum, it is preferable that the peak intensity of the light guided through the emission spectrum conversion region and the active region is ½ or more of the peak intensity of the light directly emitted from the active layer. On the other hand, since it will become narrow conversely if it is too much, it is preferable that it is twice or less.

  The length of the active region of the SLD and the emission spectrum conversion region, the amount of injected current, and the reflectance of the reflective film may be appropriately changed, and an arbitrary spectrum shape can be obtained by combining them under appropriate conditions. .

Example 4
Embodiment 4 of the present invention will be described below with reference to FIG.

  This embodiment is composed of two SLDs, each of the active regions 1801 and 1802 on the light emission side, each of the emission spectrum conversion regions 1803 and 1804 adjacent to the active region, and a high reflection provided on the opposite end surface of the light emission side. It is composed of a film 1805. By so doing, the lengths and current densities of the active regions 1801 and 1802 and the emission spectrum conversion regions 1803 and 1804 can be individually set as compared with the first embodiment. Therefore, there is an advantage that the emission spectrum can be controlled more easily.

  Also, with the configuration as shown in FIG. 18, the length of each SLD can be set individually. In this embodiment, an n-type cladding layer, an active layer, a p-type cladding layer, and a contact layer are stacked on an n-type substrate. The ridge portion of each SLD is formed using a general semiconductor lithography method and semiconductor etching. The electrodes are electrically separated by removing the Ti / Au and GaAs contact layers of the upper electrode using, for example, photolithography and wet etching. In the present embodiment, two SLDs are combined, but a structure in which three or more SLDs are combined may be employed.

(Example 5)
In this example, an example in which the amount of injected current is changed in the configuration of Example 1 is shown (FIG. 19). In Example 1, no current was injected into the emission spectrum conversion region 222, but in this example, the emission spectrum was measured when the current was changed to 1, 2, 3, 5, 10 mA. As shown in FIG. 19, it can be seen that the peak of the long wavelength component increases as the injected current increases (as the current density in the emission spectrum conversion region increases). Therefore, in the case of the configuration of the light source as in Example 1, the effect of increasing the full width at half maximum is obtained until the current injection amount into the emission spectrum conversion region 222 is about 3 mA, and becomes smaller when the current is 5 mA or more.

Claims (8)

A light source having a superluminescent diode having a plurality of light emitting regions, an emission spectrum conversion region, and a control unit for controlling a current injected into the plurality of light emission regions and the light emission spectrum conversion region,
The emission spectrum conversion region is configured to absorb and emit light having a short wavelength component among light wavelength components incident on the emission spectrum conversion region,
And one of the first light emitting Ru emitted is emitted from a region of the plurality of light emitting regions, among the plurality of light emitting regions, emitted from the different second emission region and the first emission region , through the emission spectrum transform domain, further a light to emit through the first light-emitting area, is configured such but is emitted are combined,
The control unit causes the current density of the second light emitting region to be smaller than the current density of the first light emitting region, and a reverse bias voltage is applied to the light emission spectrum conversion region to inject current. As described above, the light source is characterized by controlling the current to be injected into the emission spectrum conversion region and the plurality of light emission regions. The light source according to claim 1 , wherein the emission spectrum conversion region has a waveguide structure. The light source according to claim 2, wherein the waveguide structure has a ridge structure. The light source according to claim 3, wherein the ridge structure is formed so as to be inclined with respect to a normal to a light emission end face of the light source. 5. The light source according to claim 1, wherein an absorption region where no voltage is applied is provided between the first light emitting region and a light emission end face of the light source. The light source according to claim 1, wherein the first light emitting region, the light emission spectrum conversion region, and the second light emitting region have a common active layer. The light source according to any one of claims 1 to 6, wherein the active layer has a quantum well structure, and an emission wavelength of the quantum well structure is in a range of 800 nm to 900 nm. A light source according to any one of claims 1 to 7 ,
An interference optical system that divides the light from the light source into an irradiation light for irradiating the object and a reference light, and generates an interference light by the reflected light and the reference light irradiated on the object;
A wavelength dispersion unit for wavelength-dispersing the interference light;
A light detection unit that receives the interference light wavelength-dispersed;
An information acquisition unit for acquiring information on the object based on the intensity of the interference light;
An optical coherence tomographic imaging apparatus comprising:

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